The ATM Switch Model The B-ISDN envisioned by ITU-T is expected to support a heterogeneous set of narrowband and broadband services by sharing as much as possible the functionalities provided by a unique underlying transport layer based on the ATM characteristics. As already discussed in Section , two distinctive features characterize an ATM network: (i) the user information is transferred through the network in small fixed-size packets, called cells1, each 53 bytes long, divided into a payload (48 bytes) for the user information and a header (5 bytes) for control data; (ii) the transfer mode of user information is connection-oriented, that. | Switching Theory Architecture and Performance in Broadband ATM Networks Achille Pattavina Copyright 1998 John Wiley Sons Ltd ISBNs 0-471-96338-0 Hardback 0-470-84191-5 Electronic Chapter 5 The ATM Switch Model The B-ISDN envisioned by ITU-T is expected to support a heterogeneous set of narrowband and broadband services by sharing as much as possible the functionalities provided by a unique underlying transport layer based on the ATM characteristics. As already discussed in Section two distinctive features characterize an ATM network i the user information is transferred through the network in small fixed-size packets called cells1 each 53 bytes long divided into a payload 48 bytes for the user information and a header 5 bytes for control data ii the transfer mode of user information is connection-oriented that is cells are transferred onto virtual links previously set up and identified by a label carried in the cell header. Therefore from the standpoint of the switching functions performed by a network node two different sets of actions can be identified operations accomplished at virtual call set up time and functions performed at cell transmission time. At call set-up time a network node receives from its upstream node or user-network interface UNI a request to set up a virtual call to a given end-user with certain traffic characteristics. The node performs a connection acceptance control procedure not investigated here and if the call is accepted the call request is forwarded to the downstream node or UNI of the destination end-user. What is important here is to focus on the actions executed within the node in preparation of the next transfer of ATM cells on the virtual connection just set up. The identifier of the virtual connection entering the switching node carried by the call request packet is used as a new entry in the routing table to be used during the data phase for the new virtual connection. The node updates the table by associating to that .
