UTRAN (UMTS Terrestrial Radio Access Network)

UTRAN, short for UMTS Terrestrial Radio Access Network, is a collective term for the Node-B's and Radio Network Controllers which make up the UMTS radio access network. This communications network, commonly referred to as 3G (for 3rd Generation Wireless Mobile Communication Technology), can carry many traffic types from real-time Circuit Switched to IP based Packet Switched. The UTRAN allows connectivity between the UE (user equipment) and the core network. See also GERAN. The UTRAN contains the base stations, which are called Node Bs, and Radio Network Controllers (RNC). The RNC provides control functionalities for one or more Node Bs. A Node B and an RNC can be the same device, although typical implementations have a separate RNC located in a central office serving multiple Node B's. Despite the fact that they do not have to be physically separated, there is a logical interface between them known as the Iub. The RNC and its corresponding Node Bs are called the Radio Network Subsystem (RNS). There can be more than one RNS present in an UTRAN.

UTRAN architecture

There are four interfaces connecting the UTRAN internally or externally to other functional entities: Iu, Uu, Iub and Iur. The Iu interface is an external interface that connects the RNC to the Core Network (CN). The Uu is also external, connecting the Node B with the User Equipment (UE). The Iub is an internal interface connecting the RNC with the Node B. And at last there is the Iur interface which is an internal interface most of the time, but can, exceptionally be an external interface too for some network architectures. The Iur connects two RNCs with each other.

HS-DSCH ( High-Speed Downlink Shared Channel )

High-Speed Downlink Shared Channel (HS-DSCH) is used in HSDPA (UMTS) to send packets on the downlink to the UEs. It is called High-Speed to distinguish it from the more general definition of the downlink shared channel (DSCH) in UMTS. (The latter channel is sometimes referred to as Release'99 DSCH.)

Node-B ( UMTS )

Node-B is a term used in UMTS (Universal Mobile Telecommunications System) to denote the BTS (base transceiver station). In contrast with GSM base stations, Node B uses WCDMA as air transport technology. As in all cellular systems, such as UMTS and GSM, Node B contains radio frequency transmitter(s) and the receiver(s) used to communicate directly with the mobiles, which move freely around it.

Node B is the physical unit for radio transmission/reception with cells. Depending on sectoring (omni/sector cells), one or more cells may be served by a Node B. A single Node B can support both FDD and TDD modes, and it can be co-located with a GSM BTS to reduce implementation costs. Node B connects with the UE via the W–CDMA Uu radio interface and with the RNC via the Iub asynchronous transfer mode (ATM)–based interface. Node B is the ATM termination point.

The main task of Node B is the conversion of data to and from the Uu radio interface, including forward error correction (FEC), rate adaptation, W–CDMA spreading/despreading, and quadrature phase shift keying (QPSK) modulation on the air interface. It measures quality and strength of the connection and determines the frame error rate (FER), transmitting these data to the RNC as a measurement report for handover and macro diversity combining. The Node B is also responsible for the FDD softer handover. This micro diversity combining is carried out independently, eliminating the need for additional transmission capacity in the Iub.

The Node B also participates in power control, as it enables the UE to adjust its power using downlink (DL) transmission power control (TPC) commands via the inner-loop power control on the basis of uplink (UL) TPC information. The predefined values for inner-loop power control are derived from the RNC via outer-loop power control.

Uu

In UMTS radio interface between the UE ( User Equipment ) and the Node-B (3G BTS ( Base Transceiver Station ) is called Uu.

UE ( User Equipment ) - UMTS

UE is the Universal Mobile Telecommunications System (UMTS) term. IS UMTS user equipment ( UE ) is any device used directly by an end user to communicate. It can be a hand-held telephone, a card in a laptop computer, or other device. It connects to the base station ("Node-B", or 3G Base Transceiver Station) as specified in the 25-series of specifications.
It roughly corresponds to the mobile station in GSM systems.

UE handles the following tasks towards the core network:

• Mobility management
• Call control
• Session management
• Identity management

The corresponding protocols are transmitted transparently via a Node-B(UMTS BTS), that is, Node-B does not change, use or understand the information. These protocols are also referred to as Non-access stratum protocols.

Backbone router ( OSPF )

These are routers that are part of the OSPF backbone. By definition, this includes all area border routers, since those routers pass routing information between areas. However, a backbone router may also be a router that connects only to other backbone (or area border) routers, and is therefore not part of any area (other than Area 0).

To summarize: an area border router is always also a backbone router, but a backbone router is not necessarily an area border router.

NSSA ( Not-So-Stubby Areas )

An OSPF stub area has no external routes in it. A NSSA allows external routes to be flooded within the area. These routes are then leaked into other areas. This is useful when you have a non-OSPF router connected to an ASBR of a NSSA. The routes are imported, and flooded throughout the area. However, external routes from other areas still do not enter the NSSA.

Stub Areas

Stub areas are areas that do not propagate AS external advertisements. By not propagating AS external advertisements, the size of the topological databases is reduced on the internal routers of a stub area. This in turn reduces the processing power and the memory requirements of the internal routers.

ASBR ( Autonomous System Boundary Routers )

A router that exchanges routing information with routers belonging to other Autonomous Systems. Such a router has AS external routes that are advertised throughout the Autonomous System. The path to each AS boundary router is known by every router in the AS. This classification is completely independent of the previous classifications: AS boundary routers may be internal or area border routers, and may or may not participate in the backbone.

Area border Routers

A router that attaches to multiple areas. Area border routers run multiple copies of the basic algorithm, one copy for each attached area and an additional copy for the backbone. Area border routers condense the topological information of their attached areas for distribution to the backbone. The backbone in turn distributes the information to the other areas.

BDR ( Backup designated router )

A backup designated router (BDR) is a router that becomes the designated router if the current designated router has a problem or fails. The BDR is the OSPF router with second highest priority at the time of the last election.

RID ( Router ID )

RID is the highest logical ( loopback ) IP address configured on a router, if no logical/loopback IP address is set then the Router uses the highest IP address configured on its active interfaces. (e.g. 192.168.0.9 would be higher than 10.1.0.10).

DR ( Designated Router )

A designated router (DR) is the router interface elected among all routers on a particular multiaccess network segment, generally assumed to be broadcast multiaccess. Special techniques, often vendor-dependent, may be needed to support the DR function on nonbroadcast multiaccess (NBMA) media. It is usually wise to configure the individual virtual circuits of a NBMA subnet as individual point-to-point lines; the techniques used are implementation-dependent.

Do not confuse the DR with an OSPF router type. A given physical router can have some interfaces that are designated, others that are backup designated (BDR), and others that are non-designated. If no router is DR or BDR on a given subnet, the BDR is first elected, and then a second election is held if there is more than one BDR. The router winning the second election becomes DR, or, if there is no other BDR, designates itself DR. The DR is elected based on the following default criteria:

• If the priority setting on a OSPF router is set to 0, that means it can NEVER become a DR or BDR (Backup Designated Router).
• When a DR fails and the BDR takes over, there is another election to see who becomes the replacement BDR.
• The router sending the Hello packets with the highest priority wins the election.
• If two or more routers tie with the highest priority setting, the router sending the Hello with the highest RID (Router ID) wins. NOTE: a RID is the highest logical (loopback) IP address configured on a router, if no logical/loopback IP address is set then the Router uses the highest IP address configured on its active interfaces. (e.g. 192.168.0.1 would be higher than 10.1.1.2).
• Usually the router with the second highest priority number becomes the BDR.
• The priority values range between 0 - 254, with a higher value increasing its chances of becoming DR or BDR.
• IF a HIGHER priority OSPF router comes online AFTER the election has taken place, it will not become DR or BDR until (at least) the DR and BDR fail.
• If the current DR 'goes down' the current BDR becomes the new DR and a new election takes place to find another BDR. If the new DR then 'goes down' and the original DR is now available, it then becomes DR again, but no change is made to the current BDR.

DR's exist for the purpose of reducing network traffic by providing a source for routing updates, the DR maintains a complete topology table of the network and sends the updates to the other routers via multicast. This way all the routers do not have to constantly update each other, and can rather get all their updates from a single source. The use of multicasting further reduces the network load. DRs and BDRs are always setup/elected on Broadcast networks (Ethernet). DR's can also be elected on NBMA (Non-Broadcast Multi-Access) networks such as Frame Relay or ATM. DRs or BDRs are not elected on point-to-point links (such as a point-to-point WAN connection) because the two routers on either sides of the link must become fully adjacent and the bandwidth between them cannot be further optimized.

LSA ( Link state advertisement )

The Link-state advertisement (LSA) is a basic communication means of the OSPF routing protocol for IP. It transports router's local routing topology to all other local routers in the same OSPF area. OSPF is designed for scalability, so some LSAs are not flooded out on all interfaces, but only on those that belong to the appropriate area or those that have been elected as designated router. In this way detailed information can be kept localized, while summary information is flooded to the rest of the network.

For all types of LSAs, there are 20-byte LSA headers. One of the fields of the LSA header is the link-state ID.

The opaqure LSAs, types 9, 10, and 11, are designated for future upgrades to OSPF for application-specific purposes. For example, Cisco Systems uses opaqure LSAs for Multiprotocol Label Switching (MPLS) with OSPF. Standard LSDB flooding mechanisms are used for distribution of opaque LSAs. Each of the three types has a different flooding scope.

Each router link is defined as one of four types: type 1, 2, 3, or 4. The LSA includes a link ID field that identifies, by the network number and mask, the object that this link connects to.

Depending on the type, the link ID has different meanings.

• link type 1

Link type 1 is a point-to-point connection to another router. Its link ID is the neighboring router ID.

• link type 2

Link type 2 is a connection to a transit network. Its link ID is the IP address of DR.

• link type 3

Link type 3 is a connection to a stub network. Its link ID is the IP network/subnet number.

• link type 4

Link type 4 is a virtual link. Its link ID is the neighboring router ID.

The LSA types defined in OSPF are as follows:

• Type 1 - Router LSA - the router lists the links to other routers or networks in the same area, together with the metric. Type 1 LSAs are flooded across their own area only. The link-state ID of the type 1 LSA is the originating router ID.

• Type 2 - Network LSA - the designated router on a broadcast segment (e.g. Ethernet) lists which routers are joined together by the segment. Type 2 LSAs are flooded across their own area only. The link-state ID of the type 2 LSA is the IP interface address of the DR.

• Type 3 - Summary LSA - an Area Border Router (ABR) takes information it has learned on one of its attached areas and summarizes it before sending it out on other areas it is connected to. This helps scalability by removing detailed topology information for other areas, because their routing information is summarized into just an address prefix and metric. The summarization process can also be configured to remove a lot of detailed address prefixes and replace them with a single summary prefix, also helping scalability. The link-state ID is the destination network number for type 3 LSAs.

• Type 4 - ASBR-Summary LSA - this is needed because Type 5 External LSAs are flooded to all areas and the detailed next-hop information may not be available in those other areas. This is solved by an Area Border Router flooding the information for the router (i.e. the Autonomous System Border Router) where the type 5 originated. The link-state ID is the router ID of the described ASBR for type 4 LSAs.

• Type 5 - External LSA - these LSAs contain information imported into OSPF from other routing processes. They are flooded to all areas (except stub areas). For "External Type 1" LSAs routing decisions are made by adding the OSPF metric to get to the ASBR and the external metric from there on, while for "External Type 2" LSAs only the external metric is used. The link-state ID of the type 5 LSA is the external network number.

• Type 6 - Group Membership LSA - this was defined for Multicast extensions to OSPF (MOSPF), a multicast routing protocol which is not in general use.

• Type 7 - Routers in a Not-so-stubby-area (NSSA) do not receive external LSAs from Area Border Routers, but are allowed to send external routing information for redistribution. They use type 7 LSAs to tell the ABRs about these external routes, which the Area Border Router then translates to type 5 external LSAs and floods as normal to the rest of the OSPF network.

• Type 8 - a link-local only LSA for the IPv6 version of OSPF, which is known as OSPFv3. A type 8 LSA is used to give information about link-local addresses and a list of IPv6 addresses on the link. Type 8 is a specialized LSA that is used in internetworking OSPF and Border Gateway Protocol (BGP).

• Type 9 - a link-local "opaque" LSA (defined by RFC2370) in OSPFv2 and the Inter-Area-Prefix LSA in OSPFv3.

• Type 10 - an area-local "opaque" LSA as defined by RFC2370. Opaque LSAs contain information which should be flooded by other routers even if the router is not able to understand the extended information itself. Typically type 10 LSAs are used for traffic engineering extensions to OSPF, flooding extra information about links beyond just their metric, such as link bandwidth and color.

• Type 11 - an "opaque" LSA defined by RFC2370, which is flooded everywhere except stub areas. This is the opaque equivalent of the type 5 external LSA.

SPF Algorithm ( in OSPF )

The Shortest Path First (SPF) routing algorithm is the basis for OSPF operations. When an SPF router is powered up, it initializes its routing-protocol data structures and then waits for indications from lower-layer protocols that its interfaces are functional.

After a router is assured that its interfaces are functioning, it uses the OSPF Hello protocol to acquire neighbors, which are routers with interfaces to a common network. The router sends hello packets to its neighbors and receives their hello packets. In addition to helping acquire neighbors, hello packets also act as keepalives to let routers know that other routers are still functional.

On multiaccess networks (networks supporting more than two routers), the Hello protocol elects a designated router and a backup designated router. Among other things, the designated router is responsible for generating LSAs for the entire multiaccess network. Designated routers allow a reduction in network traffic and in the size of the topological database.

When the link-state databases of two neighboring routers are synchronized, the routers are said to be adjacent. On multiaccess networks, the designated router determines which routers should become adjacent. Topological databases are synchronized between pairs of adjacent routers. Adjacencies control the distribution of routing-protocol packets, which are sent and received only on adjacencies.

Each router periodically sends an LSA to provide information on a router's adjacencies or to inform others when a router's state changes. By comparing established adjacencies to link states, failed routers can be detected quickly, and the network's topology can be altered appropriately. From the topological database generated from LSAs, each router calculates a shortest-path tree, with itself as root. The shortest-path tree, in turn, yields a routing table.

OSPF Packet Format

All OSPF packets begin with a 24-byte header, as illustrated in Figure

The following descriptions summarize the header fields illustrated in Figure 46-2.

•Version number—Identifies the OSPF version used.

•Type—Identifies the OSPF packet type as one of the following:

–Hello—Establishes and maintains neighbor relationships.

–Database description—Describes the contents of the topological database. These messages are exchanged when an adjacency is initialized.

–Link-state request—Requests pieces of the topological database from neighbor routers. These messages are exchanged after a router discovers (by examining database-description packets) that parts of its topological database are outdated.

–Link-state update—Responds to a link-state request packet. These messages also are used for the regular dispersal of LSAs. Several LSAs can be included within a single link-state update packet.

–Link-state acknowledgment—Acknowledges link-state update packets.

•Packet length—Specifies the packet length, including the OSPF header, in bytes.

•Router ID—Identifies the source of the packet.

•Area ID—Identifies the area to which the packet belongs. All OSPF packets are associated with a single area.

•Checksum—Checks the entire packet contents for any damage suffered in transit.

•Authentication type—Contains the authentication type. All OSPF protocol exchanges are authenticated. The authentication type is configurable on per-area basis.

•Authentication—Contains authentication information.

•Data—Contains encapsulated upper-layer information.

OSPF ( Open Shortest Path First )

Open Shortest Path First (OSPF) is a routing protocol developed for Internet Protocol (IP) networks by the Interior Gateway Protocol (IGP) working group of the Internet Engineering Task Force (IETF). The working group was formed in 1988 to design an IGP based on the Shortest Path First (SPF) algorithm for use in the Internet. Similar to the Interior Gateway Routing Protocol (IGRP), OSPF was created because in the mid-1980s, the Routing Information Protocol (RIP) was increasingly incapable of serving large, heterogeneous internetworks.

OSPF is a link-state routing protocol that calls for the sending of link-state advertisements (LSAs) to all other routers within the same hierarchical area. Information on attached interfaces, metrics used, and other variables is included in OSPF LSAs. As OSPF routers accumulate link-state information, they use the SPF algorithm to calculate the shortest path to each node.

OSPF was derived from several research efforts, including Bolt, Beranek, and Newman's (BBN's) SPF algorithm developed in 1978 for the ARPANET (a landmark packet-switching network developed in the early 1970s by BBN), Dr. Radia Perlman's research on fault-tolerant broadcasting of routing information (1988), BBN's work on area routing (1986), and an early version of OSI's Intermediate System-to-Intermediate System (IS-IS) routing protocol.

OSPF has two primary characteristics.
The first is that the protocol is open, which means that its specification is in the public domain. The OSPF specification is published as Request For Comments (RFC) 1247.
The second principal characteristic is that OSPF is based on the SPF algorithm, which sometimes is referred to as the Dijkstra algorithm, named for the person credited with its creation.

Zener Diode

A particular type of semiconductor which acts as a normal rectifier until the voltage applied to it reaches a certain point, or threshold voltage. At this point — at the "Zener voltage", "avalanche voltage" or "Zener knee voltage" — the Zener diode becomes either conducting (i.e., "turns on") or non-conducting (i.e., "turns off"). These types of circuits include computer equipment (turn on), voice-activated circuits such as telephone wiretap devices (turn on), and surge protectors (turn off). As the main use of a Zener diode is to provide a reference voltage, it often is known as a "reference diode". In a RF (Radio Frequency) clamp application, the Zener diode is used to clamp (i.e., supply) a specific voltage for other, protected components, perhaps in an integrated circuit (IC). The Zener diode is the device that made it possible to make digital integrated circuits. Without Zener diode on-chip reference voltage (and, thereby, the benefit of voltage regulation and transient voltage protection), we would not be able to just "hook them together", as we do now.


Figure: a) Current versus voltage of a zener diode and b) schematic symbol for a zener diode

Zen Mail

Email messages that arrive with no text in the message body.

ZDSF ( Zero Dispersion Shifted Fiber )

A type of Dispersion Shifted Fiber ( DSF ) that is used in long haul, high speed fiber optical transmission systems. ZDSF shifts that interface to the point that chromatic dispersion and waveguide dispersion cancel each other out at 1550nm (nanometers), rather than the 1310nm window used in NDSF ( Non Zero Dispersion Shifted Fiber ).