Channel

Channel connections provide direct channel attachment to a mainframe and are significantly faster than 802.2 DLC connections. There are two types of channel connections: older bus and tag channel connections, which can reach speeds of up to 4.5 MB per second, and newer ESCON connections, which can reach speeds approaching 17 MB per second. Support for channel connections is limited to adapters supported natively through SNA Server.

Bus & tag channel attachments use parallel copper cable and offer a flexible, high-speed mainframe connection solution. Many hardware vendors produce SNA Open Gateway Architecture (SOGA)-compliant bus and tag products, allowing you to choose a solution that best fits your needs.

ESCON (Enterprise System Connection) channel attachments use standard fiber cable and increase throughput significantly. ESCON is the best choice for high-performance, high-bandwidth connections. ESCON is currently the fastest host connection method available between SNA Server computers and mainframe systems.

ESCON is an ideal connection method in centralized or distributed deployments where high performance and responsiveness is required by users.

Table 4.3 summarizes all common connection methods that can be used with SNA Server:

Table 4.3 Connection methods

Method	Throughput	Characteristics
Token ring	4 or 16 Mbps	Midrange performance using DLC protocol. Supports multiple host connections using a single adapter. Easy and inexpensive to implement. Suitable for a wide range of purposes.
Ethernet	10 Mbps	Midrange performance using DLC protocol. Supports multiple host connections using a single adapter. Easy and inexpensive to implement. Suitable for light to medium network traffic conditions.
FDDI	100 Mbps	High performance using DLC protocol. Supports multiple host connections using a single adapter. Relatively expensive to implement. Suitable for higher-performance connections.
SDLC	9600 - 19200 bps	Low performance using SDLC protocol. Supports 254 sessions over a single host connection. Easy and inexpensive to implement. Suitable for low-traffic WAN connections.
X.25	9600 - 19200 bps	Low performance using QLLC protocol. Supports 254 sessions over a single host connection. Easy and inexpensive to implement. Suitable for low-traffic WAN connections.
DFT	2.35 Mbps	Low to midrange performance. Supports five sessions over a single host connection. Inexpensive. Suitable for environments with an existing DFT-based infrastructure.
Twinax	1 Mbps	Low performance. Supports five sessions over a single host connection. Inexpensive. Suitable for AS/400 host environments with an existing twinax infrastructure.
Channel - Bus & Tag	4.5 MBytes/s	High performance. Supports a high number of host connections. Expensive. Suitable for high-performance connections.
Channel - ESCON	17 MBytes/s	Highest performance. Supports a high number of host connections. Expensive. Suitable for conditions where maximum throughput is required.