character encoding (see Unicode). Routing data and other metadata is additional to the payload size. Larger content (concatenated SMS, multipart or segmented SMS, or "long SMS") can be sent using multiple messages, in which case each message will start with a User Data Header (UDH) containing segmentation information. Since UDH is part of the payload, the number of available characters per segment is lower: 153 for 7-bit encoding, 134 for 8-bit encoding and 67 for 16-bit encoding. The receiving handset is then responsible for reassembling the message and presenting it to the user as one long message. While the standard theoretically permits up to 255 segments, 10 segments is the practical maximum with some carriers, and long messages are often billed as equivalent to multiple SMS messages. In some cases 127 segments are supported, but software limitations in some SMS applications do not permit this. Some providers have offered length-oriented pricing schemes for messages, although that type of pricing structure is rapidly disappearing. Gateway providers SMS gateway providers facilitate SMS traffic between businesses and mobile subscribers, including SMS for enterprises, content delivery, and entertainment services involving SMS, e.g. TV voting. Considering SMS messaging performance and cost, as well as the level of messaging services, SMS gateway providers can be classified as aggregators or SS7 providers. The aggregator model is based on multiple agreements with mobile carriers to exchange two-way SMS traffic into and out of the operator's SMSC, also known as "local termination model". Aggregators lack direct access into the SS7 protocol, which is the protocol where the SMS messages are exchanged. SMS messages are delivered to the operator's SMSC, but not the subscriber's handset; the SMSC takes care of further handling of the message through the SS7 network. Another type of SMS gateway provider is based on SS7 connectivity to route SMS messages, also known as "international termination model". The advantage of this model is the ability to route data directly through SS7, which gives the provider total control and visibility of the complete path during SMS routing. This means SMS messages can be sent directly to and from recipients without having to go through the SMSCs of other mobile operators. Therefore, it is possible to avoid delays and message losses, offering full delivery guarantees of messages and optimized routing. This model is particularly efficient when used in mission-critical messaging and SMS used in corporate communications. Moreover, these SMS